Rotor for dynamoelectric machines



June 8, 1954 M. w. BRAINARD 2,680,822

ROTOR FOR DYNAMOELECTRIC MACHINES Filed June 25, 1951 3 Sheets-Sheet 1/6 K e3 A 6 Q o a f6 e 3e a a /e IN VEN TOR.

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June 8, 1954 .M. w. BRAINARD 2,680,822

ROTOR FOR DYNAMOELECTRIC MACHINES Filed June 25, 1951 3 Sheets-Sheet 2INVENTOR. Maar/be lf/.ra/na/Q/ June 8, 1954 M. w. BRAINARD ROTOR FORDYNAMOELECTRIC MACHINES 5 Sheets-Sheet 5 Filed June 25, 1951 INVENTOR.Maar/e M Era/hard Patented June 8, 1954 UNITED .STATES PAT ENT OFFICE.KOTOR FOR DYNAMOELECTRIC MACHINES .Maurice W. Brainard, Los Angeles,Calif., as-

. signor of ene-:half to OKeefe & Merritt Com- ,.pa'ny, Losv Angeles,Calif., azcorporation of California Application `June 25, 1951, SerialNo. 233,421

(Cl. S10-e261) .13 Claims. l

invention. Ahas to do with `a vrotorwand method Vof mahingthe saine, andmore speii callyit is concerned with a'rotor for electric machine, forinstance, where magnets v@ir-"other such elements are involvedfandare-"requiredto 'be organized in -a stable assembly snbjectfto`rotation. It is a general-object of this inventionto provide a simple,practical, and effective 4rotor construction andft'o Iprovide a simple,practical, easily executed method -ofY making such a cone struction..

`Rotors such as are employed in electric-machines, as Where magnets-orother elements are required vto be carried i-n lan assemblyv`wl'iichfisI to be rotated, present certa-in structural problems and itis highly-desirable, in practice, v-to provide such astructure havingthe desiredelements -or mag-nets assembledina rigid, permanentstructure, together with pole piecesl or other parts, so that thereis noplay or wor-king `Abetween the pantser elements and Aso vthat thevelectricaly or magrneticactionv involved is handled erliciently.

Itis a 'general object of thisv invention to provide a rotor of thegeneral characterereferredto, for .example, a lrotor for Iari-electricmachine wherein magnets, pole'pieces, andotherpar'ts, are .assembledintoa-perinanent, rigid unit; and wherein the desired pressureengagement is es tablished between the `partsby forced ltleforn-1ationof .an element.

y-tris another object `of 'thek invention lto provide a rotoreoi thegeneral character .referred to Wherein the...el'ement deformed toestablish the `desired tight relationship lof parts :is in the nature-oa sleeve `or acore` at fthe :center of the rotor, yand thisecore issuchfthat it may serve asthefmeans hy which asupporting shaft-is held.

It is another .object of this invention toy provide arotor .of .thegeneralcharacter ref-erredto in which the element deformed to .gain thedesiredtight relationship.l :ofparts is inthe nature oi a core. heldpositively in the-idesiredrdeformed oonditionby the .shaft that supportsthe rotor iny the machine.

.it is another object fof' thefinvention to provide a :deformable coreyfor a rotorzof the .generale-liaracter :referred to, which. .core liszof` simple, 'inexpensiveconstruction.and such that.itcanfberreadil-ydefo-rmed 'inthe ydesired:mann-er, which may .serve.asfthe mountingelement by which Fthe rotor iscarriedeon a shaft.

.Another :object of the inventionis .to provide afmethod for the:.making `,of a 'rotorzof the general. characterretemfedazto/Whichmethod* is characterized by the deformation of an elexnent ni.

2 the rotor .in the course of assembly of the parts, tothe end that thedeformedelement maintains the general assembly tight or with the variouspartsY in pressure engagement with each-other.

It is another object of this invention to provide a method of thegeneral character referred to which is exceedingly simple in .executionand which can be carried out without employing complicated or specialequipment and without vresorting to operations likely to in any waydamage or impair the parts involved.

The invention can be used to advantage in rotors for electricalmachines, and therefore, I Will make specific reference to forms orembodiments of the invention `wherein parts are concerne-d whichassemble to form the-rotor 4of a generator. ln setting forth theinvention I will refer tothe rotor as involving permanent magnetsvwhichare combined with pole pieces suitable for cooperation with a iixedannular armature, vor the like.

In a typical machine employing the rotor vthere may be a cases-carryingan annular iixed armature and having end caps carry-ing bearing-s Whichsupport a shaft centrally of the armature. The shaft may 4be consideredas a vpart ofthe rotor and. has a middle portion which is straight andturned vand -on that `portion of the shaft there is afframe that may beformed of apl-urality -of rigid, dat plates,- spaced apart axially ofthe machine. The plates of the frame may be tied together by tie rods,andthere may be inner tie rodsconnecting the plates near the shaft, andouter tie rods extending between the `peripheral portions of the plates.Peripheral pole pieces are carried by the framebetyeen the peripheralportions of the plates of the frame, and they are spacedcircumferentially `of Athe rotor linan annularseries concentric with theshaft. The outer perfipheries of the-pole pieces-may be curvedconcentric With the shaft While the inner parts of the pole pieces areformed to present channels that `face inwardly or :tow-ard the shaft.vThe outer tie rods of the frame extend snugly through the outer polepieces and, as a result, the pole pieces are clamped tightk between theplates of the frame to become solid or rigid withthe trame.

A plurali-ty of magnets is incorporated in `the rotor Vand :arerectangular :in cross sectionand there is one located .immediatelyvinn/tard of each ofthe outer pole'. pieces, Athemagnets being engagedorAseated in the c'lfiannels of the `pole pieces. The :magnets projectinwardfrom theiouter pole pieces and their :inner portions vcooperate to:dene` azpolygonalxcentra-l opening that ',carriesa core supported bythe shaft. The core is a continuous annularl element substantiallycoextensive with the magnets and it may :be either solid or laminated.The core has outer faces that flt against the inner sides of the magnetsand has shaft seats engaging the exterior of the straight turned portionof the shaft. Openings extend inwardly in the core from the magnet seatsand, in effect, divide the core into corner portions which form magneticties between adjacent magnets and connections that extend between andconnect adjacent corner portions. rIhe openings that thus characterizethe core have enlarged round portions that freely pass the inner tierods of the frame and which form the connecting portions so that theyare arcuate or bridge-lilac.

The core is initially formed so that the shaft receiving opening issomewhat smaller in diam eter than the exterior of the straight turnedportion of the shaft. In a typical. case the shaft is initially formedthe straight turned portion of a given diameter and adjacent one endthereof there is a ered part. The frame is initially assembled with theouter core pieces tightly in place and the magnets are arranged againstthe inner sides of the outer pole pieces, following which the core isinserted in the opening defined by the magnets, the core being formed sothat in its initial condition it will insert easily into the openingformed by the magnets. The tapered end portion of the shaft is theninserted into the core and forced through it, as the core as a whole isexpanded, the connecting portions of the core being deformed or pressedoutwardly by the wedging action of the tapered part of the shaft. Theexpansion or outward deformation of the core is such as to enlarge thecore generally causing the magnet seats of the core to be pressedtightly against the magnets so that the magnets in turn are pressedtightly against the outer core pieces, which are held fixed by theframe. The insertion of the shaft is continued until the straight turnedportion occurs within the core and extends throughout the length of thecore, making the core tight or solid on the shaft as well as tight inthe assembly of magnets held by the assembly of outer pole pieces.

The major deformation occurs in the core to allow for the desiredexpansion thereof at the connecting portions between the cornerportions. The corner portions wedge tight into the magnet assembly withthe magnet seats of the core tight against the inner ends of themagnets. When the principal parts have been assembled, any openings orinterstices occurring in the structure, as between magnets, pole pieces,or the unoccupied openings ibetween the core, are nlled with a suitablefiller, as by a pressing or casting operation, to the end that thefinished rotor is solid and without cavities.

The various objects and features of my invention will be fullyunderstood from the following detailed description of typical preferredforms and applications of the invention, throughout which descriptionreference is made to the accompanying drawings, in which:

Fig. 1 is a longitudinal sectional View of a rotary machine such as apermanent magnet generator, in which the rotor of the machinecharacterized by an annular assembly of permanent magnets employs theconstruction provided by the present invention. Fig. 2 is a detailedtransverse sectional View of the machine shown in Fig. l, being a Viewtaken as indicated by line 2-2 on Fig. 1. Fig. 3 is a perspective viewof the shaft employed in the machine or in the rotor of the machine,showing it in the condition or form in which it may be employed for thedeformation of the core, as provided by the present invention. Fig. 4 isa perspective view of the expansible core of the rotor, as provided bythe present invention, showing a form thereof which is of laminatedconstruction. Fig. 5 is a detailed transverse sectional view of parts ofthe rotor assembled ready for reception of the shaft, the core beingshown in place within the assembly of magnets and before it has beenexpanded or deformed. Fig. 6 is a view similar to Fig. 5, showing theshaft in place after the core has been expanded and with the shaftmaintaining the core in the expanded condition. Fig. 'I is an enlargedView of a portion of Fig. 5. Fig. 8 is an enlarged view of a portion ofFig. 6. Figs. 9 to l5, inclusive, illustrate another form ofconstruction wherein the core is formed of a solid lbody of material ormetal. Fig. 9 illustrates the core in an initial form, for instance aform in which it occurs following its initial formation. Fig. 10 is aperspective view of the core shown in Fig. 9, showing it collapsed orhaving been pressed into a collapsed condition. Fig. 1l is a transversesectional View of a rotor showing the collapsed core illustrated in Fig.l0 in place in the opening defined by the annular assembly of magnets.Fig. 12 is a view similar to Fig. 11 showing a shaft in the expandedcore. Fig. 13 is an enlarged view of a portion of Fig. 9. Fig. 14 is anenlarged View of a portion of Fig. li, and lig. 15 is an enlarged f viewof a portion of Fig. l2.

The particular electric machine illustrated in the drawings is agenerator and it is shown as involving a case A, a fixed or stationaryarmature B in the case, and a rotor C operating within the armature Band carried by or including a shaft S carried by bearings D supported bythe case. Since the present invention is in no way concerned with thegeneralities of the electric machine, but rather, is concerned with therotor and its manufacture, a simple machine construction is illustratedand will serve merely as an example of a typical machine construction inwhich the invention can be used.

The case A illustrated in the drawings involves a main central part orbody itl which is a rigid annular element, and end caps Il secured to orcarried by the ends of the body it and having central portions i2 whichcarry the bearings D.

The armature is shown carried by the body le of the case and isillustrated as involving a laminated core assembly ill having inwardlyprojecting teeth l5 defining slots in which suitable coils or windingsle are located. rhe various elements or parts of the armature form anannular assembly concentric with the Shaft S.

The shaft S shown in its finished form in Fig. 1 of the drawingsinvolves a central portion 2l) which is straight and round incross-section. End portions 2l project from the ends of the centralportion 2e and are carried by the bearings D supported by the end capsIl of the case. In the particular case illustrated the end portions 2lare turned down or of reduced diameter, and the bearings D are shown asanti-friction bearings suitably supported in the central portions l2 ofthe end caps il. lt is to be understood, of course, that the shaft mayhave an extension 22, for instance, a part projecting from one of theend parts 2| projecting from the exterior of the machine.

The rotor, -as provided infth'e present 'invention may'he Aconsideredas'mount-ed -on or as includingf-the-shait S, and it includes,generally, a

frame F," outer pole pieces '-G, magnets H, a core y plates involvedinAthe lrotor will 'depend' -uponthe type of construction employed, forinstance, if the'rotorinvolves "but a single annular Agroup of magnets,Vouter polepieces, anda singlelaminated core assembly, there need beonly'two 'plates 30, whereas'iin a Anrrultiple construction such' 'as isshown -in 'the drawings and where there is more than one annular seriesof magnets, and more than fone annular series' of outer pole pieces andmore'than one core, there'are plates provided so that there is a plate'between each annular series o'i"elements involved inthe rotor as Well asaplate'in each end of the assembly.

The frame includes, in addition 'to the plates 3'l'l't'ie` rods whichjoin or connect the plates, and inthe 'case -illustrated there are innertie rods 32 that connect vvthe plates '3'0 adjacent the shaft, and outer"tie rods "33 'that connect'the outer or peripheral portions of theplates as Where the plates carry'lthe outer pole pieces G. In practice asuitable number of tie .rods ris employed to gain vthe desired strengthand rigidity, and the tie rods are suitably secured or anchored to theplates involved in the frame. In 'the particular case villustrated thereare more o-utertie rods than inner tie rods, and the outer tie rods aresomewhat 'lighter in construction than the inner tie rods.

The outer pole pieces G occur or are .carried between the plates 30 ofthe frame and are spaced apart crcum'ferentially to form an annularseries oi pole pieces at the .periphery of the rotor, .adjacent polepieces G Vbeing spaced apart as clearly shown in `Fig. 2 of thedrawings. In-the preferred construction the outer pole pieces G aresecured and anchored in the -:traine by outer tier rods '.33 .of theframe. As shown lin the drawings it "is preferred that each outer polepiece G be held by a plurality o'i'outer tie rods 33 so that the outerVpole .pieces are solidly anchored to .or

in the rvframe making the assembly formed bythe 'frame and outer polepieces a solid, rigid structure that is rigid on the shaft'iS.

"In accordance 'with the invention lit is preferredthat the pole piecesG have their outer peripheries Sicuri/ed 4concentric with the shaft 'Sand each pole pieceG is'provi'ded at its inner side with aninwardlyfacing'channe'lt, andthe channels-L38 are Ypreferably 'disposed sothatthey extend axiallyof the rotor.

*Theimagnetsl illustrated'in the drawings are,

for 'purpose of simplicity, illustrated as'permanent magnets, and areshown as lbeing rectangular in cross-sectional 'coniiguration and veachhas 'its outer end portion seated lin va channel 3S of a polepiece1G,--as clearly illustrated in Fig. 2o'f`the drawings. lThere lis amagnet H for each pole piece i.Cth'andfasa-result of this rrelationshipor parts .'-the' ymagnets -form an annular vassembly oriseries. The.inner-most Vor end" portions sof the magnets I-I- closely .approachea'chother, so `that CTI theannular "series of magnets 'inuefect forms-apolygonal-opening concentric with' thesha'it 1S and/accommodating thecore J.

In the preferredconstruction the magnets are coextensive with the polepieces G 4axial-lysoi the rotor, and they -are'contined against :axialmovement or shifting by vlthe plates itt oifthe rra-Ine. The 'core J',as provided bythe present invention, ais vanv annular or ysleeve-likeelement surrounding the vrn-i'ddle yor central portion -22-0 of theshaft `and located Vinthe polygonal opening deiined'by the'-annularseries of/lmagne'ts H. In accordancewith the invention the`lcore is' provided at its exterior with outwardly facing.maglnet-seated!) andat fits interior withinwardly facing shaft-seats4I. The magnetrseats 240 lare formed orzshaped to correspond Cto theinner ends of the 'magnets H so'that they ihave 'ettective seating orhearingengagement With-the magnets andfthey are 'preferably-continuousvfrom onefend of ythe-core tothe-other, so `that the magnets are engaged-continuously from one end to. the=other'. The shaftseats -i 'faceinwardly or toward the central portion i of the shaft and, in practice,they may be varied inform or sha-pe. 'Foretrample, `as 'shown in theYcore illustrated Lon 'sheet 2 of Althefdrafwings, they are curved tohave; 'iin effect, line engagement with -al part initially 1inserted -inthe core, whereas inthe core villustr'ated on sheet 3 of the drawings,they 'are-shaped tto extend around the axisof the rotor concentric withthe shaft to have 'initialengagement-with 'a member insertedi-n the corecircumferentially ofthe core, as wel-l as longitudinal-ly thereof.

Y A feature of the core provided rby Lthe present invention is itscontinuous annular construction, it rbei-ng preferred that it be-constructed--so=that it is continuous `annularly, at 'the-saine timeibeing expansible.

In the preferred form -of lcore construction openings-extendinwardly inlthe core `from fits criterion-preferably-irom the-centers ofthe -mag'-net 'seats 4D, and these openings extendy a sub'- sta-ntial ldistanceinwardly 'and 'terminate shortly before reaching Athe interior of -thefcore where the shaft seats occur. Through Ithis cons-truction the 4coreis-'divided into corner portions each of -W-hich Ahas-contact with twoymagnets, and'connecting portions 5-| which extend :between andoonnectfthe corner portions at the 'interior of the core. In thepreferred` construction the inwardly extending openings Lhave outerportions 52' which arev straight and radially disposed'frelati-ve to theaxis of the rotor, and have inner portions 53 whichare round'an'd ofsubstantial size; andare so Arelated to the interior of the core wherethe 'shaft -sea-ts '4i occur as to `esta-hlish the connecting portions'5i 'as elongate 'bands which are, in effect, arcuate or 'arch-.likeinformation, asY clearly illustrated .in the drawings.Thestraight'openngsi2 are preferablynarrow'or mere slit-like openings,whereas the round por tions 53 lare preferably of such .size 'as toaccommo'date or passt-he inner tie rods32 of the frame with''substantial clearance', as Vshown 'throughout the drawings.

In "the 'form of .the invention 'illustrated 5in vFigs.4to:8;inclus'ive,'the core is of laminated construction, Athat is,it'ismade up' of va `Apluralityfof superimposed plates each .of which is a`continuou'sannular .elementandthe assembly of plates is 'of such extentaxially of the rotor as to :be substantially'coextensive with` 'thelmagnet assenibly andit is held between 'the inner portions of theplates 30 which are tied together by the inner tie rods 32 and 33. Incarrying out the invention it is preferred to form the core or theplates of the core of metal, for instance, of a steel, that is subjectto being deformed but is possessed of a reasonable degree of resilience.

In accordance with the invention the core J formed as above described,and as shown throughout the drawings, is inserted in the assembly madeup of the frame, outer core pieces, and magnets, with the core in a formin which the annular series of shaft seats [il at the interior thereofestablishes an opening of a diameter somewhat smaller than the middleportion Eil of the shaft S.

In a typical manner of carrying out the invention the shaft may beinitially employed in a form such as is shown in Fig. 3, where it hasthe central portion 2% turned or otherwise nished, so that it isstraight and round in cross section and of the desired sise, while ithas one end X plain and unfinished and the other end Y extending fromthe portion 2t and tapered or convergent, as shown in Fig. 3. r[hetapered end Y of the shaft element such as is shown in Fig. is insertedin the core and forced through the core from one end thereof, with theresult that it engages the core seats li and forces these parts or theconnecting portions 5i outwardly, causing general expansion of the core,and its deforma tion from the form illustrated in Figs. 5 and 7 to thatillustrated in Figs. 5 and 8. It will be readily apparent that bysuitably relating the shaft and core, or by providing a suitable initialrelationship between these elements, a deformation is effected byinsertion of the shaft which causes forced expansion or deformation ofthe core in a manner to expand the core outwardly in the annularassembly of magnets, with conse-quent outward forcing or pressing of themagnets against the fixed outer pole pieces G.

In the particular case illustrated on sheet 2 of the drawings thedeformation or expansion of the core may result in varying the form ofthe connecting portions 5i so that the shaft seats alt, which areinitially convex faces facing the shaft, are finally concave, as shownin Fig. 8. In the case of a laminated core the wedging or deformationthat occurs as the shaft is inserted with cause each individuallamination to be expanded or deformed, with consequent individual ttingthereof to the shaft. When the shaft, as shown in Fig. 3, is fullyinserted, that is, when the straight turned portion 2li is broughtcompletely Within the core, the end portions X and Y project beyond theends of the core and are accessible so that they can be readily dressedor turned to give the shaft a final form such as is illustrated in Fig.l of the drawings. As an alternate method, the expansion may be done bya special tool followed by insertion of the shaft.

In carrying out the invention it is preferred to form the frame partsand at least the plates of the frame of non-magnetic material such, forexample, as a metal that is non-magnetic, and it will be understood thatwith the core construction that I have provided the corner portions 50of the core occur in the rotor so that each corner portion is in contactwith two adjacent magnets and, consequently, forms an effective magnetictie between such magnets. It is to be understood, of course, that thecore that I have provided is formed of a material effective as aconductor of magnetism so that the magnetic tying action of the cornerportions of the core is highly efficient.

lil

It is preferred, in practice, that a rotor constructed as hereinabovedescribed, be provided with a filler K before it is put into use. Thefiller may be a suitable non-magnetic material such as a soft metal castor otherwise applied to the assembly forming the core so that all of theopenings or interstices that would otherwise be open are filled or fullyoccupied. In the partcular case illustrated portions Eil of the filler Koccur in the round openings 53 provided in the core, portions EI of thefiller occur in the narrow slits formed by the opening portions e2, andportions Si occur between adjacent magnets and adjacent outer polepieces G- and have their outer edges d3 finished to be concentric withthe curved outer edges 3?; of the pole pieces G.

On sheet 3 of the drawings I illustrate a core constructionincorporating the invention wherein the core, instead of being oflaminated construction, is solid or formed of a single solid or unitaryblock of metal. In this particular case the core J is initially formedso that the shaft seats di are concave and initially conform to theexterior of the shaft portion 2i). 'lo facilitate manufacture thestraight portions 52 of the openings in the core extending inwardly fromthe .iagnet seats lil are in the form of open slots such as can bereadily formed by a machine tool, and as thus formed and as shown inFig. l, the core is of such size that it would not enter the assembly ofmagnets included in the rotor.

The first operation performed on this core is deformation and involvescollapsing of the core to a form such as is shown in Fig. 10, where theopen slots 52 are reduced to mere cracks, with the result that the coreis reduced in over-al1 size so that it will enter the assembly ofmagnets, as shown in Fig. ll, the core can be expanded, as shown in Fig.l2, by insertion of a shaft as shown in Fig. l5, and as hereinabovedescribed, with the result that the core as a whole is expanded anddeformed, bringing the magnet seats into pressure engagement with themagnets and the magnets into pressure engagement with the outer polepieces. In this case the core can be proportioned so that the expansionwhich causes it to exert the desired pressure in the rotor need notbring it back to its original size, as shown in Fig. 9.

It will be understood and it is believed that it will be appreciatedfrom the drawings, that by suitable proportioning of the parts of thecore, and particularly the bridge-like connecting portions or the core,an expansion and deformation can be brought about in the core by theinsertion of the shaft which results in a rotor that is in the form of aunit having the several parts permanently and rigidly assembled and inpressure engagement with each other, so that the rotor can, in practice,be operated at high speeds under severe conditions and over long periodsof time without any danger whatsoever of parts working loose or shiftingwithin the rotor.

Having described only typical preferred forms and applications of myinvention, I do not wish to be limited or restricted to the specificdetails herein set forth, but wish to reserve to myself any variationsor modifications that may appear to those skilled in the art and fallwithin the scope of the following claims.

Having described my invention, I claim:

l. A. rotor including, a shaft, a frame on the shaft projecting radiallytherefrom, pole pieces at the outer peripheral portion of the frame andfixed thereto, a plurality of magnets in an annular series and seatedoutwardly against the pole 9 pieces-,land a continuous annularexpansible core tight on the shaft and held` expanded thereby and seatedoutwardly against and in pressure engagement with said magnets.

2. A'roto1"including',a shaft, a frame' on the shaft"v projectingradially therefrom, pole pieces at the outer peripheral portion of theframe and fixed relative thereto; a Vplurality. of .magnets in anannular' series and yseated. outwardly against the pole pieces, andacontinuous annular expansiblecore tight on the shaftr and seatedAoutwardly against said magnets in pressure engagement therewith, thecore having circumferentially spaced portions at its outer peripheryeach bearing outwardly against two adjacent magnets and havingcircumferentially spaced shaft seats at its inner periphery and hearingon the shaft.

3. A rotor including, a shaft, a frame on the shaft projecting radiallytherefrom, pole pieces at the outer peripheral portion of the frame andfixed relative thereto, a plurality of magnets in an annular series andseated outwardly against the pole pieces, and a continuous annularexpansible core including a plurality of plates arranged side by sideand engaged one against another and each bearing tightly in against theshaft and bearing tightly out against the magnets.

4. A rotor including, a shaft, a frame on the shaft projecting radiallytherefrom, pole pieces at the outer peripheral portion of the frame andfixed relative thereto, a plurality of relatively movable elements in anannular series and seated outwardly against the pole pieces, and acontinuous annular expansible core tight on the shaft and seatedoutwardly against said elements in pressure engagement therewith, theframe including plates engaged on the shaft and spaced apart axiallythereof and the said elements and core being held between the plates.

5. A rotor including, a shaft, a frame on the shaft projecting radiallytherefrom, pole pieces at the outer peripheral portion of the frame andfixed relative thereto, a plurality of elements in an annular series andseated outwardly against the pole pieces, and a continuous annularexpansible core tight on the shaft and seated outwardly against saidelements in pressure engagement therewith, the frame including platesengaged on the shaft and spaced apart axially thereof and tie rodsextending between the plates and through the pole pieces, the saidelements and core being held. between the plates.

6. A rotor including, a shaft, a frame on the shaft projecting radiallytherefrom, pole pieces at the outer peripheral portion of the frame andfixed relative thereto, a plurality of elements in an aimular series andseated outwardly against the pole pieces, and a continuous annularexpansible core tight on the shaft and bearing inwardly thereon andseated outwardly against said elements and bearing outwardly thereon,the frame inciuding plates engaged on the shaft and spaced apart axiallythereof and outer tie rods extending between the plates and through thepole pieces and inner tie rods extending between the plates and throughthe core, the said elements and core being held bet reen the plates.

T. A rotor including, a shaft, a frame on the shaft projecting radiallytherefrom, pole pieces at the outer peripheral portion of the frame andfixed relative thereto, a plurality of elements in an annular series andseated outwardly against the pole pieces and bearing outwardly thereon,and an expansible core tight on the shaft and seated outwardly againstsaid' elements and bearing outwardly thereon, the frame including platesengaged on the shaft and spaced apart axially thereof and outer-tierodsextending between the plates and through the pole pieces and innertie rods extending between the plates and through the core, the polepieces having openings snugly receiving. the outer tie rods and the corehaving openings freely passing the inner tie rods.

8. A rotor including, a shaft, a frame on the shaft projecting radiallytherefrom, pole pieces at the outer peripheral portion of the frame andxed relative thereto, a plurality of elements in an annular series andseated outwardly against the pole pieces, and an expansible core tighton the shaft and seated outwardly against said elements in pressureengagement therewith, the core eing a continuous annular' structure withaxially disposed openings in it entering it from its outer periphery anddividing it into corner portions each engaging two adjacent elements andhaving connecting portions between and connecting the corner portionsand each with a part bearing on the shaft.

9. A rotor including, a shaft, a frame on the shaft projecting radiallytherefrom, pole pieces at the outer peripheral portion of the frame andfixed relative thereto, a plurality of elements in an annular series andseated outwardly against the pole pieces, and an expansible core tighton the shaft and seated outwardly against said elements, the core beinga continuous annular structure with axially disposed openings in itextending into it from its outer periphery and dividing it into cornerportions each engaging two adjacent elernents and having bridge-shapedportions between and connecting the corner portions and each with a partbearing on the shaft.

10. A rotor including, a shaft, a frame on the shaft projecting radiallytherefrom, pole pieces at the outer peripheral portion of the frame andxed relative thereto, a plurality of elements in an annular series andseated outwardly against the pole pieces and defining a polygonalopening concentric with the shaft, and a continuous` annular expansiblecore with a polygonal exterior fitting the opening and withcircumferentially spaced parts bearing inward on the shaft, the exteriorof the core being divided into separate corner portions each wedgedoutwardly into engagement with two adjacent elements.

11. A rotor including, a shaft, a frame on the shaft projecting radiallytherefrom, pole pieces at the outer peripheral portion of the frame andxed relative thereto, a plurality of magnets in an annular series andseated outwardly against the pole pieces, and an expansible coreincluding a solid continuous annulal1 core with portions bearing tightinward against the shaft and portions bearing tight outward against themag nets.

12. A rotor including, a shaft, a frame on the shaft projecting radiallytherefrom, pole pieces at the outer peripheral portion of the frame andfixed relative thereto, a plurality of elements in an annular series andseated outwardly against the pole pieces, and an expansible core tighton the shaft and seated outwardly against said ele ments, the frameincluding plates engaged on the shaft and spaced apart axially thereofand tie rods extending between the plates, the core having openingsextending into it from its exterior dividing it into portions eachbearing out against two adjacent elements and having circumferentialiyspaced parts bearing inwardly References Cited in the le of this patent0n the each Opepng having Slot-Shaped outer portion and having a roundinner portlon freely passing a tie rod of the frame. Number Name Date13. A continuous expansibie polygonal rotor 5 9391910 Hassler NOV' 91909 core having separated outer pol-tions with mag- 119961946 Beep Apr-9 1935 net seats thereon and inner portions connecting 4931102 Bramal'dJan' 3 1950 the outer portions at the interior of the core and FOREIGNPATENTS having shaft seats thereon, the connecting por- Numbe Countr Dte tions being deformable to canse spreading 01": the 10 459595 GreatBritgin Jans), 1937 outer portmns radially and cucumferentlally. 495 813Great Britain N0v 21 1938

